18,046 research outputs found

    Conclusion: Rethinking African Governance and Development

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    This article draws together the main strands of argument being developed by the Africa Power and Politics Programme (APPP), as reflected in this IDS Bulletin. The central question is what kinds of governance arrangements work better to support the provision of the public goods that are essential to sustained and inclusive development in Africa. Evidence at local, sectoral and national levels is pointing to the overall conclusion that what works is often a ‘practical hybrid’, combining authoritative coordination with local problem?solving and constructive borrowing from local cultural repertoires. Consistent with the general idea of ‘going with the grain’, we find that the most likely source of the necessary vertical discipline is a developmental form of neo?patrimonialism, not ‘good governance’, as currently conceived. Similarly, local collective action to address bottlenecks in public goods provision is seldom enhanced by standard donor and NGO approaches to citizen or client empowerment

    Gravitational instabilities in a protosolar-like disc - I. Dynamics and chemistry

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    MGE gratefully acknowledges a studentship from the European Research Council (ERC; project PALs 320620). JDI gratefully acknowledges funding from the European Union FP7-2011 under grant agreement no. 284405. ACB's contribution was supported, in part, by The University of British Columbia and the Canada Research Chairs program. PC and TWH acknowledge the financial support of the European Research Council (ERC; project PALs 320620).To date, most simulations of the chemistry in protoplanetary discs have used 1 + 1D or 2D axisymmetric α-disc models to determine chemical compositions within young systems. This assumption is inappropriate for non-axisymmetric, gravitationally unstable discs, which may be a significant stage in early protoplanetary disc evolution. Using 3D radiative hydrodynamics, we have modelled the physical and chemical evolution of a 0.17 M⊙ self-gravitating disc over a period of 2000 yr. The 0.8 M⊙ central protostar is likely to evolve into a solar-like star, and hence this Class 0 or early Class I young stellar object may be analogous to our early Solar system. Shocks driven by gravitational instabilities enhance the desorption rates, which dominate the changes in gas-phase fractional abundances for most species. We find that at the end of the simulation, a number of species distinctly trace the spiral structure of our relatively low-mass disc, particularly CN. We compare our simulation to that of a more massive disc, and conclude that mass differences between gravitationally unstable discs may not have a strong impact on the chemical composition. We find that over the duration of our simulation, successive shock heating has a permanent effect on the abundances of HNO, CN and NH3, which may have significant implications for both simulations and observations. We also find that HCO+ may be a useful tracer of disc mass. We conclude that gravitational instabilities induced in lower mass discs can significantly, and permanently, affect the chemical evolution, and that observations with high-resolution instruments such as Atacama Large Millimeter/submillimeter Array (ALMA) offer a promising means of characterizing gravitational instabilities in protosolar discs.Publisher PDFPeer reviewe

    Doomed drones? Using passage experiments and mathematical modelling to determine Deformed wing virus population dynamics in male honey bees

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    Funding: This research was funded by the BBSRC (Biotechnology and Biological Sciences Research Council), grant numbers: BB/M010996/1 and BB/R00305X/1. P.C.S was supported by the BBSRC, grant number: BB/S00243X/1.Varroa destructor is an ectoparasitic mite of honeybees which vectors a range of pathogenic viruses, the most notable being Deformed wing virus (DWV). Mites parasitise bees during pupal development and male honeybees, drones, have a longer development cycle than female workers (24 versus 21 days), allow for more progeny mites to develop per foundress (1.6–2.5 compared to 0.7–1.45). How this longer exposure time influences evolution of the transmitted virus population is unknown. Using uniquely tagged viruses recovered from cDNA we investigated the replication, competition and morbidity of DWV genotypes in drones. Assays examining virus replication and morbidity revealed drones are highly susceptible to both predominant genotypes of DWV. In virus passage studies using an equimolar inocula of major DNA genotypes and their recombinants, the recombinant form dominated but did not reach 100% of the virus population within 10 passages. Using an in-silico model of the virus–mite–bee system we examined bottlenecks during virus acquisition by the mite and subsequent injection of viruses into the host, which may play a significant role in shaping virus diversity. This study furthers our understanding of the variables influencing DWV diversity changes and provides insight into areas of future research in the mite–virus–bee system.Publisher PDFPeer reviewe

    Poly(A)-binding proteins: multifunctional scaffolds for the post-transcriptional control of gene expression

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    Most eukaryotic mRNAs are subject to considerable post-transcriptional modification, including capping, splicing, and polyadenylation. The process of polyadenylation adds a 3' poly(A) tail and provides the mRNA with a binding site for a major class of regulatory factors, the poly(A)-binding proteins (PABPs). These highly conserved polypeptides are found only in eukaryotes; single-celled eukaryotes each have a single PABP, whereas humans have five and Arabidopis has eight. They typically bind poly(A) using one or more RNA-recognition motifs, globular domains common to numerous other eukaryotic RNA-binding proteins. Although they lack catalytic activity, PABPs have several roles in mediating gene expression. Nuclear PABPs are necessary for the synthesis of the poly(A) tail, regulating its ultimate length and stimulating maturation of the mRNA. Association with PABP is also a requirement for some mRNAs to be exported from the nucleus. In the cytoplasm, PABPs facilitate the formation of the 'closed loop' structure of the messenger ribonucleoprotein particle that is crucial for additional PABP activities that promote translation initiation and termination, recycling of ribosomes, and stability of the mRNA. Collectively, these sequential nuclear and cytoplasmic contributions comprise a cycle in which PABPs and the poly(A) tail first create and then eliminate a network of cis- acting interactions that control mRNA function

    A library of infectious hepatitis C viruses with engineered mutations in the E2 gene reveals growth-adaptive mutations that modulate interactions with scavenger receptor class B type I

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    While natural hepatitis C virus (HCV) infection results in highly diverse quasispecies of related viruses over time, mutations accumulate more slowly in tissue culture, in part because of the inefficiency of replication in cells. To create a highly diverse population of HCV particles in cell culture and identify novel growth-enhancing mutations, we engineered a library of infectious HCV with all codons represented at most positions in the ectodomain of the E2 gene. We identified many putative growth-adaptive mutations and selected nine highly represented E2 mutants for further study: Q412R, T416R, S449P, T563V, A579R, L619T, V626S, K632T, and L644I. We evaluated these mutants for changes in particle-to-infectious-unit ratio, sensitivity to neutralizing antibody or CD81 large extracellular loop (CD81-LEL) inhibition, entry factor usage, and buoyant density profiles. Q412R, T416R, S449P, T563V, and L619T were neutralized more efficiently by anti-E2 antibodies and T416R, T563V, and L619T by CD81-LEL. Remarkably, all nine variants showed reduced dependence on scavenger receptor class B type I (SR-BI) for infection. This shift from SR-BI usage did not correlate with a change in the buoyant density profiles of the variants, suggesting an altered E2-SR-BI interaction rather than changes in the virus-associated lipoprotein-E2 interaction. Our results demonstrate that residues influencing SR-BI usage are distributed across E2 and support the development of large-scale mutagenesis studies to identify viral variants with unique functional properties. IMPORTANCE Characterizing variant viruses can reveal new information about the life cycle of HCV and the roles played by different viral genes. However, it is difficult to recapitulate high levels of diversity in the laboratory because of limitations in the HCV culture system. To overcome this limitation, we engineered a library of mutations into the E2 gene in the context of an infectious clone of the virus. We used this library of viruses to identify nine mutations that enhance the growth rate of HCV. These growth-enhancing mutations reduced the dependence on a key entry receptor, SR-BI. By generating a highly diverse library of infectious HCV, we mapped regions of the E2 protein that influence a key virus-host interaction and provide proof of principle for the generation of large-scale mutant libraries for the study of pathogens with great sequence variability

    The Role of Legal Services in the Antipoverty Program

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    Large-scale adaptive radiations might explain the runaway success of a minority of extant vertebrate clades. This hypothesis predicts, among other things, rapid rates of morphological evolution during the early history of major groups, as lineages invade disparate ecological niches. However, few studies of adaptive radiation have included deep time data, so the links between extant diversity and major extinct radiations are unclear. The intensively studied Mesozoic dinosaur record provides a model system for such investigation, representing an ecologically diverse group that dominated terrestrial ecosystems for 170 million years. Furthermore, with 10,000 species, extant dinosaurs (birds) are the most speciose living tetrapod clade. We assembled composite trees of 614-622 Mesozoic dinosaurs/birds, and a comprehensive body mass dataset using the scaling relationship of limb bone robustness. Maximum-likelihood modelling and the node height test reveal rapid evolutionary rates and a predominance of rapid shifts among size classes in early (Triassic) dinosaurs. This indicates an early burst niche-filling pattern and contrasts with previous studies that favoured gradualistic rates. Subsequently, rates declined in most lineages, which rarely exploited new ecological niches. However, feathered maniraptoran dinosaurs (including Mesozoic birds) sustained rapid evolution from at least the Middle Jurassic, suggesting that these taxa evaded the effects of niche saturation. This indicates that a long evolutionary history of continuing ecological innovation paved the way for a second great radiation of dinosaurs, in birds. We therefore demonstrate links between the predominantly extinct deep time adaptive radiation of non-avian dinosaurs and the phenomenal diversification of birds, via continuing rapid rates of evolution along the phylogenetic stem lineage. This raises the possibility that the uneven distribution of biodiversity results not just from large-scale extrapolation of the process of adaptive radiation in a few extant clades, but also from the maintenance of evolvability on vast time scales across the history of life, in key lineages

    Ladino clover for Ohio farms

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